1. Field of the Invention
The invention relates to a high performance electrode made from a dilute nickel alloy containing alloying additions of zirconium and boron that is temperature, oxidation, sulfidation and fracture resistant and, more particularly, toward an electrode for an ignition device, such as a spark plug for an internal combustion engine, furnace, or the like.
2. Related Art
A spark plug is a spark ignition device that extends into the combustion chamber of an internal combustion engine and produces a spark to ignite a mixture of air and fuel. Recent developments in engine technology are resulting in higher operating temperatures to achieve improved engine efficiency. These higher operating temperatures, however, are pushing the spark plug electrodes to the very limits of their material capabilities. Presently, Ni-based nickel-iron-chromium alloys specified under UNS N06600, such as those sold under the trade names Inconel 600®, Nicrofer 7615®, and Ferrochronin 600®, as well as various dilute nickel alloys, are in widespread use as spark plug electrode materials. Dilute nickel alloys are high nickel alloys, having nickel contents that are generally greater than 90% by weight of the alloy, with small amounts of varying alloying elements, such as silicon, aluminum, yttrium, chromium, titanium, cobalt, tungsten, molybdenum, niobium, vanadium, copper, calcium, manganese and the like, to improve the high temperature properties over that of pure nickel, including enhanced resistance to high temperature oxidation, sulfidation and associated corrosive wear, as well as deformation, cracking and fracture associated with cyclic thermo-mechanical stresses resulting from operation of these devices.
As is well known, the resistance to high temperature oxidation of these dilute nickel alloys decreases as their operating temperature increases. Since combustion environments are highly oxidizing, corrosive wear including deformation and fracture caused by high temperature oxidation and sulfidation can result and is particularly exacerbated at the highest operating temperatures. At the upper limits of operating temperature (e.g., 1400° F.), tensile, creep rupture and fatigue strength also have been observed to decrease significantly which can result in deformation, cracking and fracture of the electrodes. Depending on the electrode design, specific operating conditions and other factors, these high temperature phenomena may contribute individually and collectively to undesirable growth of the spark plug gap and diminished performance of the ignition device and associated engine. In extreme cases, failure of the electrode, ignition device and associated engine can result from electrode deformation and fracture resulting from these high temperature phenomena. These failure modes and effects can be particularly problematic in competitive applications, such as racing engines.
Accordingly, there is a need for high performance electrodes made from dilute nickel alloys having improved resistance to high temperature oxidation, sulfidation and related corrosive wear, as well as improved high temperature tensile, creep rupture and fatigue strength and resistance to cracking and fracture.